Extensible conductor



Nov. 22, 1949 w. DUTCHER EXTENSIBLE CONDUCTOR Fi 'led June 7, 1944 7 M r m mm m M: 8 w .2\ .Wu Q F Z 1 L .w 7 3 F 1 Patented Nov. 1949 UNITED STATES PATENT OFFICE 2,488,527 EXTENSIBLE CONDUCTOR Harold William Butcher, Lebanon. N. H.

Application June 7, 1944, Serial No. 539,168

A (Cl. 174-69) (Granted under the act of March 3, 1883, as

amended April 30, T928: 370 0. G. 757) 3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalties thereon.

The present invention concerns an extensible electrical conductor which retains all its electrical characteristics particularly its ability to transmit substantially undistorted audio and radio frequency currents while its physical length is varied.

It is an object of the invention to provide an electrical conductor which can be stretched, being both extensible and contractible.

It is an object oi the invention to provide a means whereby communication can be main: tained between a towing aircraft and a glider while the two are connected by a tow rope made of nylon or the like which has extensible and contrac ible characteristics. Such means may be made an integral part of the towrope or may be externally attached thereto.

It is an object of the invention to provide an extensible and contractible electrical conductor with a central core of rubber and having the conductor material in the form of a helix, loose braiding or the like on the outside thereof.

Other objects will appear as the specification proceeds.

In the drawing like numbers refer to like parts, however for clarity substantially identical part will be referred to by different numbers in different forms of the invention.

Figure 1 is an elevation of one form of basic conductor with one end turned into the plane of pro ection and sectioned.

Figure 2 is an elevation of a rope with an end turned into the plane of projection and sectioned, showing the conductor of Figure 1 incorporated as an integral part.

Figure 3 is a side elevation of a separate con ductor shielding means. I

Figure 4 is an end view from the left, of the conductor and shield section coupling of Figure 3.

Figure 5 is a plan of a binding or belaying strap.

Figure 6 is a side elevation of a portion of tow rope with the conductor and shield of Figure 3 attached.

Figure 7 is a cross section on the line 1-1 of Figure 6.

One form the invention may take comprises a central live rubber core which may be stranded or solid. Around this core are braided strands of high gage copper wire or the like combined with acetate yarn interlaced to form a reverse helix or herringbone pattern. Good results are obtained by using eight strands of wire and eight of acetate yarn. The assembly is in turn covered by a'tubular layer or coating of rubber insulation having an extensibility approximating that of the central rubber core. This insulation may be a separate tube surrounding the braid. The conductor strands may be tinned or given some other metallic coating resistant to corrosion so that the conductance between adjacent touching conductors is maintained.

It has been found that the use of the braiding step instead of the single helix for the conductor materially decreases the resistance and increases its strength. Also the network formed by the intersecting conductor strands has a much smaller inductance than a single helix. These advantages are gained at some loss in extensibility. Accordingly where conductor extensibility of several hundred percent is required the "pure" helical form may be preferable. A plurality of conductor strands may be connected in parallel if desired.

Where the conductor is to be utilised to maintain intercommunication or control between a towship and a glider it is preferably incorporated in the towing rope as an integral part thereof. Three such conductors are customarily used and are made the heart strand of the three secondary sections which make up the main rope. Where it is desired to apply this type of conductor to towing ropes which are already laid up, the extensible conductor is customarily fastened to the outside of the towing rope. For this purpose it is advisable to loosely shield the extensible conductor by means of a closely wound helix of tempered heavier wire. Sections of these shielding helices are joined by ferrules having flanges with which the wire of the shielding helix is interthreaded. The flanges may then be strapped to a towing cable by ordinary strap and buckle means.

Referring to the drawing:

Solid rubber core II) has braided there around alternate strands of tin coated 4O SWG copper wire II and cellulose acetate yarn l2. A rubber tubular coating l3 surrounds the braided strands H and i2 and forms an insulated conductor M. This conductor can be used for most applications where radio, telephone or even light power circuits are required. As the amperage increases it will of course be necessary to utilise larger strands I 3 tion in extensibility'and resilience. It will be seen that should the conductor be stretched, rubber core II will aid in maintaining the formation of strands II and I2 and by virtue of its resilience return them to their original position when the stretching force is removed or reduced. These strands though braided may be thought of as a group of individual helices the pitch of which increases as the conductor 14 is stretched. It may be understood from an inspection of Figure 1 that an exceedingly loose relation is developed between the wire strands H of the braid since they are not required to pass alternately under and over each other, but comprise two sets which tend to lie in separate cylindrical concentric forms, except as they may be bent to some extent, if at all, by the interwoven cellulose acetate or other yarn strands ii. That is to say, one set of metal strands lies inwardly of the other at all intersections, and the yarn being the more flexible, it will yield the most in the weaving, so that the wires will be'bent in a minimum degree. This adds greatly to the freedom of movement of the wires in accommodating themselves to increased or decreased pitch of their windings, incident to extension and contraction of the conductor unit as a whole. The resilience of the acetate yarn will have the effect of accommodating tendencies to development of unequal stresses in the wires H by yielding of the acetate, and the latter capability will also aid in retraction of the conductor to its original dimensions when relieved of stretching loads.

The conductors It may be incorporated in a rope or cable I 6 as shown in Figure 2. Cable I! may be of wire, sisal or like material. The conductor I 4 however functions to best advantage when cable 15 is of relatively yielding material such as nylon Such cables are used extensively in towing gliders or the like in the air where they experience extensions in excess of 20% of normal length, and it is necessary to maintain communication or control circuits throughout such filights.

Where a cable such as 20 is already laid up without conductors ll incorporated as an integral part thereof, conductors It may be assoclated therewith as shown in Figure 6. The conductors M are surrounded by a helical wire shield ll of about 24 SWG, which is interthreaded with flanges I! on a ferrule l8. Flanges H have a slanted opening 19 which allows a portion ill of shield I to be threaded therethrough.

A belay strap 2| provided with a tongue portion 22 and notches 23 is fastened around the body of ferrule II and cable 15. The end of tongue portion 22 is threaded through loop 24 and drawn tight. The associated projecting portions II of notches 23 bear against loop 24 and hold the assembly tightly bound together at points about 20 inches apart. Shield I! has no electrical connection with conductors 14, but stretches with them as cable It eiongates under load.

I claim:

1. An extensible conductor for attachment to extensible tow cables, comprising an elastic extensible and inherently retractive core member, a spiral wire conductor element formed thereon, an encircling insulation enclosing the spiral wire conductor element, an extensible external shield comprising a closed helix of wire formed without and around said insulation and attachable means to join one such helix coaxially to another like helix to form a longitudinally continuous shield throughout a communication line constituted by said conductor.

2. The structure of claim 1 wherein said attachable means consists of a tubular ferrule insertable within opposed ends of two of said helices, said ferrule having a spiral rib thereon at each end to fit between convolutions of respective said ends and oppose separation of the helices and ferrule.

3. The structure of claim 2 wherein said spiral ribs are separated a substantial distance longitudinally of the ferrule to afford a space between ends of coengaged shield sections, a belay strap insertable through a cable rope and constructed to be bent around a cable strand and said ferrule between shield sections thereon, and means to lock the strap in coengagement with said shield and cable.

HAROLD WILLIAM BUTCHER.

REFERENCES CITED The following references are of record in the die of this patent: 

